I took the people to each represent continents - Africa, Europe, Asia, and the Americas. So, I don’t see “Irish” as much as I see “European”. I took the theme to be showing how similar and connected we all are (via the thread).

The hint of colonialism / exploitation I see is that the European woman is holding her candle (representing culture) without fear, while the other 3 are cautiously protecting theirs, having dealt with attempts by others to extinguish them.

There was a study done to answer this exact question - I read it several years ago though so I can't remember what it was called. I believe it took place in conjunction with testing people in enclosed environments, such as those you'd see on a ship headed to Mars. They were kept in a space where they were deliberately were unable to tell night from day (plus no clocks, calendars, etc). I remember it being found that people tended to default to wake/sleep cycles longer than 24 hours, but I don't remember how much longer. Two days? I'm having difficulty finding it, but obviously NASA is extremely interested in this question as well.